1. Field of the Invention
The present invention relates to a piezoelectric substance and a manufacturing method thereof, a piezoelectric substance and a liquid discharge head using such a piezoelectric element, and a liquid discharge apparatus.
2. Description of the Related Art
In recent years, piezoelectric actuators have been watched as new motors in place of electromagnetic motors in a portable information equipment field and chemical and medical field, in the point that motors can be miniaturized and be arranged with high density. During the operation, the piezoelectric actuator does not generate electromagnetic noise and is not influenced by noise. Further, the piezoelectric actuator has been watched as a technique for manufacturing equipment of sub-millimeter class as represented by a micro machine, and a minute piezoelectric element has been requested as a drive source of the equipment.
In general, the piezoelectric element is generally manufactured by forming a sintered piece or a single crystal piece of a bulk material obtained by applying heat treatment to the piezoelectric substance into a minute shape having desired dimension and thickness, by means of a technique such as cutting, polishing and the like. Further, when the minute piezoelectric element is formed, generally, the piezoelectric element is directly formed by coating a green sheet-shaped piezoelectric substance at a predetermined position on a metal or silicon substrate and burning the piezoelectric substance, by using a printing method or the like. The article formed from such a green sheet has a thickness of about several tens of μm to several hundreds of μm and electrodes are disposed above and below the piezoelectric substance and voltage is applied via the electrodes.
In the past, the minute piezoelectric element as used in a liquid discharge head was minutely-formed from the piezoelectric substance of bulk material by using the above-mentioned technique such as cutting, polishing or the like or was manufactured by using the green sheet-shaped piezoelectric substance. An example of an apparatus using such a piezoelectric element includes, for example, a liquid discharge head having a piezoelectric element structure of unimorph type. The liquid discharge head comprises pressure chambers in communication with ink supply chambers and ink discharge ports in communication with the respective pressure chambers and constructed so that a vibrating plate to which the piezoelectric element is joined or on which the piezoelectric element is directly formed is situated within each pressure chamber. With this arrangement, by applying predetermined voltage to the piezoelectric element to cause expansion and contraction of the piezoelectric element, flexion vibration is generated to compress ink in the pressure chamber, thereby discharging an ink droplet from the ink discharge port.
Nowadays, although color ink jet printers utilizing the above-mentioned action have been popularized, enhancement of printing performance thereof, particularly higher resolving power and higher speed printing have been requested. To this end, it has been tried to achieve the high resolving power and the high speed printing by using a multi-nozzle head structure in which the liquid discharge heads are miniaturized. In order to miniaturize the liquid discharge head, it is necessary to further miniaturize the piezoelectric element for causing the discharging of the ink. Further, in recent years, the liquid discharge head has actively been tried to be applied to an industrial application, such as wiring direct drawing. In this case, it is necessary to achieve patterning of liquid having more diverse properties with a higher resolving power, and, thus, higher performance of the liquid discharge head has been requested.
In recent years, due to development of micro machine techniques, investigations for developing a super-small-sized high accurate piezoelectric element by forming the piezoelectric substance as a thin film and by using freely minute-working techniques used in a semiconductor field have been made. A thickness of the piezoelectric substance formed, particularly, by a thin film method such as a sputtering method, a chemical vapor synthesizing method, a sol-gel method, a gas deposition method, a pulse laser deposition method and the like is generally about several hundreds of nm to several tens of μm, in the application to the piezoelectric actuator. Further, electrodes are provided in association with the piezoelectric substance so that voltage is applied via the electrodes.
On the other hand, due to the miniaturization of the piezoelectric element, piezoelectric substance materials having higher performance representing a higher piezoelectric property have actively been investigated. As a material for the piezoelectric substance which has recently been watched, materials of relaxor group have been examined, and, for example, in Japanese Patent No. 3397538, a method for synthesizing lead magnesiumate niobate titanate (also referred to as PMN-PT) by flux fusing or melting is described. It has been reported that a bulk-like single crystal member can be obtained by such a synthesizing method and a material having a great strain amount exceeding 1% is obtained.
Further, it has been examined that the piezoelectric substance is formed from the material of relaxor group by using the thin film method such as the sputtering method, chemical vapor synthesizing method, sol-gel method, gas deposition method, pulse laser deposition method and the like. For example, in the document “Applications of Ferroelectrics” (2002. ISAF 2002. Proceedings of the 13th IEEE International Symposium p. 133-136), it is reported that a PMN-PT thin film was film-formed by the pulse laser deposition method (also referred to as PLD method).
However, for example, since an MEMS piezoelectric actuator which has recently been developed actively has a minute structure, if a single crystal material grown into a bulk shape as described in the above Japanese Patent No. 3397538 is used, it is necessary that the single crystal is sliced (by cutting, polishing or the like) to join the crystals together. It is difficult to apply the bulk-like single crystal material to a high accurate minute piezoelectric element. Further, also in the single crystal piezoelectric substance thin film of relaxor group formed by the thin film method, a high piezoelectric property which can be expected from the bulk-like single crystal member could not be realized and the difference therebetween is very great. Thus, in order to enhance the piezoelectric property of the single crystal piezoelectric substance thin film of relaxor group obtained by the thin film method, a further improvement in the thin film is required.